1. Field of the invention
The invention pertains to a device for cutting a pile of sheets by means of a disk-knife or revolving blade with which is associated a conveyor feeding the pile of sheets to the disk-knife while holding them between opposite clamping surfaces of two conveyor elements, at least one of which is an endless belt.
2. Description of the prior art
In what follows, the term "pile of sheets" shall mean any pile (or set) of sheets or folios which lie on top of each other, for example a book, a sheet folded several times, a booklet, a signature, etc..
The term "booklet" shall mean a pile of sheets, consisting of sheets lying on top of each other and all of which are folded around a common fold which forms the "back" of the booklet. The folios or sheets forming the booklet can be stapled or glued at the back. However, they can also be joined loosely to each other. Such a booklet may be called also a "signature".
The term "cutting a pile of sheets" shall include the so-called "trimming", in which the edges of a pile of sheets, for example the edges of a booklet, are cut, because even when only its edges are trimmed, the pile of sheets has to be cut through.
The term "elongated, flexible, endless conveyor element" is to be understood as a generic term for endless belts, strips, chains, ropes, strings, cords or the like.
The prior art shows, for example, at the delivery end of folding machines, the use of disk-knives for trimming the edges of booklets or for cutting the booklets in the middle. However, in these known devices each disk-knife has a cylindrical counter knife associated with it. The disk-knife for cutting through the booklet has a circumferential cutting edge whose cross-section is an acute angle and whose side next to the counter knife is plane. The counter knife is formed by the circumferential corner, virtually right-angled in cross-section, of a cylinder. The latter and a second cylinder, whose axis is concentric with that of the disk-knife, form a clamping-slit for the booklet. With increasing thickness of the booklet, the point at which the disk-knife starts its cut moves farther and farther away from the clamping slit in a direction opposite to the direction in which the booklet advances, so that the disk-knife must penetrate into the booklet at a point at which the booklet is not supported by the counter knife nor gripped in the clamping slit. The consequence is that, at the point of penetration of the disk-knife, the individual sheets of the booklet are not secured against displacement relative to each other. Thus, as the disk-knife penetrates into the booklet, the position of the sheets is distorted and the cut becomes necessarily more and more irregular with increasing thickness of the booklet.
With folding machines, a somewhat irregular cut has but little significance, because the booklets are usually units or sections of books (signatures), which after the binding process has been completed, are again trimmed by means of a guillotine knife.
Devices of the type just described, have been disclosed in U.S. Pat. Nos. 1,704,454 and 1,835,685. These references take the knowledge described above as point of departure, namely, that a pile of sheets cannot be cut cleanly with a disk-knife, because the disk-knife displaces the sheets relative to each other, and that, for this reason, the trimmed back of the book does not extend at a right angle to the sides of the book. (U.S. Pat. No. 1,835,685 p.2, lines 68 to 73). Therefore, in the just mentioned reference, it is proposed to use two disk-knives, arranged on opposite sides of the pile of sheets in such a manner, that the plane sides of their cutting edges point in the same direction and lie in the common cutting-plane; furthermore, each disk-knife is arranged to cut into the pile of sheets somewhat beyond the half-way line. It is apparent, that with this known device one cannot produce a cut suitable, for a visible surface, because the aforementioned device does not furnish a scissor-cut and the two cutting edges, mounted some distance apart from each other, without a counter knife, merely penetrate into the pile of sheets. For this reason, the known devices are proposed only for the trimming of backs of books, which are glued subsequently. For this purpose, a rough cut is even desirable for a better penetration of the glue. In addition, it would be pointless to produce a surface which appears clean-cut to the eye, because the backs of the books are grooved in any event to make it easier to glue on the backbone of the book, as has been brought out in the above-mentioned references.
In this known device, the conveyor consists of two parallel sections of two endless chains, made of links and bolts. These chains are provided with support members, which furnish a plane support surface when the chain section moves in a straight line. The chain links are fastened together with bolts, the ends of which are provided with rollers which move on support surfaces. This results in a very complicated conveyor, which does not lend itself to the production of a scissor-cut with a disk-knife, because the support members cannot be used as counter knives for the disk-knife, in view of the fact that this counter knife formed by the support members would be continually interrupted as the individual supports move past the disk-knife, a fact which would result in an uneven cut. Furthermore, the journals of the rollers at the ends of the bolts would be highly stressed by bending and shearing forces.
It seems that, for the above-mentioned reasons, the devices disclosed in the two cited U.S. patents have not proven themselves as means for cutting the backs of books. For that purpose, according to West German OS-publication 2,416,461 milling cutters or saws are used with a peripheral speed several times greater than the forward speed of the pile of sheets. The use of milling cutters and saws has the advantage that it avoids the high cutting pressure when the paper is sheared off which results from the tearing of the paper fiber at the cutting point. This tearing of the paper fibers results in a rought cut which is desirable for the trimming of the back of a book to be glued subsequently. In any case, none of the cited processes makes it possible to obtain a cut with a circular cutter leaving a smooth appearing edge surface on a pile of sheets, for example, on a booklet or a book.
For this reason, guillotine knives have been used exclusively until now for trimming piles of sheets, such as books, booklets, etc., whenever a smooth looking cutting surface is to be obtained. Guillotine knives furnish a very smooth, clean cut, because, in this instance, a pressure bar adjacent to the knife holds the sheets and presses them together so that they cannot shift before and while the knife penetrates into the pile. However, the guillotine cutting devices have the disadvantage that, during the cutting process, the pile of sheets to be cut must remain stationary relative to the cutting device. But this requires that the pile of sheets is brought to and removed from the cutting device in step-like fashion, which diminishes the capacity (output) of such a cutting device. To avoid this loss of capacity, decades of development of the guillotine knife have led to an elaborate cutting device disclosed in U.S. Pat. No. 3,552,246 in which the step-wise transporting of books has been eliminated by a mechanism, in which the entire guillotine cutter assembly oscillates back and forth in the direction of travel of the pile of sheets. This shows that industry did not hesitate to utilize highly advanced technical solutions to eliminate the disadvantage of intermittent transport of the pile of sheets.
It is the purpose of the present invention to obviate the aforementioned difficulties by providing a device for cutting a pile of sheets with a disk-knife, wherein the pile of sheets can be supplied to the disk-knife in uninterrupted, continuous flow and which, with a relatively simple construction will guarantee a satisfactory, smooth cut, acceptable for a visible surface.